Working on a Different Wavelength

Posted on | August 4, 2011 | No Comments

Terahertz Frequency Imaging

Terahertz Imaging System Team

  • Terahertz Imaging System Team
    From left to right: Kirk Reinbold, associate director of the Advanced Diagnostics & Therapeutics initiative at Notre Dame; Lei Liu, research assistant professor of electrical engineering; Emily Yunshan Wang and Berardi Sensale-Rodriguez, graduate students; and Huili (Grace) Xing, the Rev. John Cardinal O’Hara, C.S.C., Associate Professor of Electrical Engineering. Not pictured are Paul W. Bohn, the Arthur J. Schmitt Professor of Chemical and Biomolecular Engineering; Hsueh-Chia Chang, the Bayer Corporation Professor of Chemical and Biomolecular Engineering; Patrick Fay, professor of electrical engineering; Debdeep Jena, associate professor of electrical engineering; and Chrislyn D’Souza-Schorey, associate professor of biological sciences.

Within 10 years of Wilhelm Röntgen’s 1895 discovery of a new form of electromagnetic radiation, hospitals around the world were using X-rays to help diagnose and treat patients. The first X-ray tubes, however, were very low power and required long exposure times to the radiation — several minutes — to produce an image. Imaging technologies have evolved considerably since then and are now, according to Notre Dame researchers, on the brink of a new generation of devices and systems that would employ electromagnetic waves in the terahertz frequency, making them safer than traditional X-rays while providing more accurate images.

From dental X-rays to angiograms, one of the questions most commonly asked during a medical imaging procedure is: “How much radiation am I being exposed to?” Because they feature ionizing X-radiation, all X-rays — radiographic (still) and fluoroscopic (real-time moving) images — have the potential to damage living tissue. A Notre Dame team, led by Huili (Grace) Xing, the Rev. John Cardinal O’Hara, C.S.C., Associate Professor of Electrical Engineering; Lei Liu, research assistant professor of electrical engineering; Patrick Fay, professor of electrical engineering; and Debdeep Jena, associate professor of electrical engineering, is working to develop novel terahertz (THz) detectors, circuits, and systems that would more affordably capture high-quality images in real-time, at room temperature, and with less damage to living tissue than X-rays and greater resolution than microwave or ultrasound technologies.­

THz waves are similar to X-rays in that they are electromagnetic waves. However, they operate at a different, non-ionizing frequency, 0.1 to 10 THz, which is between the radio and optical (laser) frequencies. The development of such devices and systems is important, not only because THz based systems do not require extensive cooling equipment but also because they do not require the addition of any chemical reagents to produce images. THz technology is also ideal for medical applications because, due to their shorter wavelengths, imaging using THz waves provides higher resolution than using microwave and millimeter waves.

Grace research

The terahertz imaging system the Notre Dame team has developed pairs a broadband quasi-optical zero bias Schottky diode detector, which covers a range of 100 GHz to nearly 900 GHz, with a planar sinuous antenna that has been photolithographically fabricated on a semi-insulating silicon substrate. Using the same material on the lens eliminates the power loss to substrate modes.

Grace research image

The University’s terahertz imaging system team is also developing a portable system for real-time chemical and biological applications.

THz waves can penetrate biological tissues, fabrics, plastics, and cardboard to more accurately produce higher resolution images. Thus, the team expects they will be useful in medical applications, such as enhanced cancer diagnostics for both shallow (surface) tumors and biopsied tissue, as well as the detection and identi-fication of disease biomarkers, pathogens, and chemical toxins. They could also prove useful in other industries for safety and quality control, such as detecting surface defects in materials, impurities in pharmaceuticals, or highlighting traces of explosive elements or concealed objects in security applications.

Part of the Advanced Diagnostics and Therapeutics initiative at the University, the team has designed and demonstrated a frequency domain THz spectroscopy and imaging system based on a broadband quasi-optical zero bias Schottky diode detector. Operating from 570 to 630?GHz, the room-temperature system they have created has also performed better than current systems in characterizing biomolecule and nano-material samples. Additional experiments at other frequency bands are currently under way. The team expects to achieve a frequency range covering 0.1 to 1 THz.

In addition, the team has been awarded two grants from the National Science Foundation and two from the Office of Naval Research for the development of THz sources, detectors, mixers, and imaging systems.

Suggested Reading

Sensale-Rodriguez, Berardi; Liu, Lei; Wang, Ronghua; Zimmermann, Tom; Jena, Debdeep; and Xing, Huili (Grace), “FET THz Detectors Operating in the Quantum Capacitance Limited Region,” To be published in the International Journal of High Speed Electronics and Systems, 2011, 20, 2.

Liu, Lei; Hesler, Jeffrey L.; Weikle II, Robert M.; Wang, Tao; Fay, Patrick; and Xing, Huili (Grace), “A 570-630 GHz Frequency Domain Terahertz Spectroscopy System Based on a Broadband Quasi-optical Zero Bias Schottky Diode Detector,” To be published in the International Journal of High Speed Electronics and Systems, 2011, 20, 2.

Goodman, Kevin D.; Protasenko, Vladimir V.; Verma, Jai; Kosel, Thomas H.; Xing, Huili (Grace); and Jena, Debdeep, “Green Luminescence of InGaN Nanowires Grown on Silicon Substrates by Molecular Beam Epitaxy,” Journal of Applied Physics, 2011, 109, 084336 (10 pages).

Liu, Lei; Hesler, Jeffrey L.; Xu, Haiyong; Lichtenberger, Arthur W.; and Weikle II, Robert M., “A Broad Quasi-optical Terahertz Detector Utilizing a Zero Bias Schottky Diode,” IEEE Microwave and Wireless Components Letters, 2010, 20, 9, 504-6.< Liu, Lei; Xu, Haiyong; Lichtenberger, Arthur W.; and Weikle II, Robert M., “Integrated 585-GHz Hot-Electron Mixer Focal-Plane Arrays Based on Annular Slot Antennas for Imaging Applications,” IEEE Transactions on Microwave Theory and Techniques, 2010, 58, 7, 1943-51. Liu, Lei.; Sensale-Rodriguez, Berardi; Zhang, Ze; Zimmermann, Tom; Cao, Yu; Jena, Debdeep.; Fay, Patrick; and Xing, Huili (Grace), “Development of Microwave and Terahertz Detectors Utilizing A1N/GaN High Electron Mobility Transistors,” at the 21st?International Symposium on Space Terahertz Technology, Oxford, March 23-25, 2010. Su, Ning; Rajavel, Rajesh; Deelman, Peter; Schulman, Joel N.; and Fay, Patrick, “Sb-heterostructure Millimeter-wave Detectors with Reduced Capacitance and Noise Equivalent Power,” IEEE?Electron Device Letters, 2008, 29, 6, 536-9.

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